so OSTEOLOGY. 



The arch, and consequently the spinal canal, are small, the 

 laminEe passing almost directly inwards from the pedicles. 



An ordinary dorsal vertebra has twelve articular surfaces — viz., 

 three anterior and three posterior, as in the cervical, and three at 

 each side ; of the latter, two are for the heads of two ribs, and 

 the third for the tubercle of the anterior rib. The depressions for 

 the heads of the ribs are deepest between the anterior vertebrae, 

 and gradually grow shallower, in the two last becoming continuous 

 with the facet on the transverse process. The eighteenth segment, 

 being attached to but one rib on each side, has eight articulating 

 surfaces only. 



Viewing the dorsal vertebrae in connection, it is seen that the 

 spines diminish from the ififth backwards, and the vertebras them- 

 selves o-row narrower. The first exhibits some of the characters 

 of a cervical vertebra, and the second has a short body, with 

 transverse and anterior oblique processes formed on the same bony 

 projection, and a neural spine, short, convex anteriorly, and more 

 bent than any other in the vertebral chain. The first thirteen 

 form the skeleton of the withers, and, when well developed, the 

 height of their spines increases the surface for muscular attach- 

 meut, and also affords greater leverage. 



LUMBAR VERTEBRA. 

 (Pl. I. G.) 



These form the skeleton of the loins, and are shorter in the 

 horse in proportion to his size, than in other animals. Their 

 number is six usually, sometimes five, in the horse, six in the 

 mule, generally five in the ass, and also, it is said, in the Arab 

 horse. Their bodies, intermediate in length between the cervical 

 and the dorsal, are thick and strong, the three anterior being 

 flattened superiorly and laterally, and possessing a strongly- 

 developed median ridge ; the three posterior ones are convex 

 laterally, and flattened above and below. More motion being 

 required in the loins than in the back, the anterior extremities 

 of the centra of the lumbar vertebrae are more convex, and the 

 posterior extremities more concave than those in the dorsal 

 region. The arches enclose a large semicircular spinal canal, 

 and with one or two exceptions possess both anterior and posterior 

 notches. The neural spines are strong, broad, and flattened 

 laterally ; they incline slightly forwards, are about the same'length 



